1. Field of the Invention
This invention relates to a circuit for electrical appliances, and in particular, to a safety or test circuit which requires the presence of a proper ground and a properly wired electrical outlet if the electrical appliance is to be operated.
2. Description of the Prior Art
There exists in the prior art various ways of grounding electrical appliances such that the same will not produce any shock or be hazardous to the operator. These ground lines, however, are not effective unless the outlet is properly grounded or unless the three-wire power cord is properly wired to the appliance. Also, it is possible to bypass the ground and thus the device is potentially dangerous.
The present invention assures that the cord is properly connected to the electrically energized load of the appliance and that the ground is properly connected to the appliance. Further, the device of the present invention checks whether the receptacle for the three-wire plug on the cord is properly wired.
Electrical safety is a never ending challenge to our modern society. This is especially true with portable electric equipment with a plug cord. The inherent danger is that the operator of this equipment may be exposed to or in contact with many "ground" paths for electric current to follow. If a current leak develops the operator may well be the conductor to ground with fatal results. The main methods of countering this danger are: (1 ) utilize a third wire in the cord to act as earth ground and thus drain off any unsolicited current leak; (2) doubly insulating electric power equipment to insure against current leak; (3) utilize the neutral wire as earth ground and thus drain any current leak back to neutral which in effect may act as ground; and (4) utilize a ground fault indicator in which a current leak theoretically will disrupt current before a lethal amount of current could cause a fatality or a lack of ground visible indicator. Method No. (1) is a good method provided the electric outlet is grounded and the ground is utilized. This is very unsatisfactory for numerous reasons: (a) properly wired and grounded outlets are still not abundantly available, (b) adaptors or "cheaters" are readily available to solve the lack of the above outlets, but in so doing, the safety ground feature is bypassed or lost, and (c) the above method also utilizes the ground prong to "key" the neutral line and the current line of the outlet to the current line and neutral line of the cord. This keying feature is lost when not utilizing the ground prong when using an adaptor or "cheater". This safety feature is also lost if the electric outlet is not properly wired according to code.
Method No. 2 is fairly acceptable except where water may enter the electric device and conduct current around the insulation. This metod is also quite costly to utilize.
Method No. 3 is very unacceptable. Many attempts have been made to insure that the cord neutral wire is connected to the receptacle or outlet neutral wire. This has not been achieved. Some of the latest ungrounded outlets have different sized female jacks to correspond with different size jack prongs on the cord. This method is almost exclusively used on portable T.V. sets where neutral is utilized as a "floating ground" on the chassis of the set. An extension cord, an adaptor or any improperly wired outlet will void this method from contributing to safety. The insulated cabinet and control knobs do achieve some degree of safety against reversing the current wire and neutral wire within the chassis. Loss of an insulated knob or bolting of the chassis to an exterior metal mounting bracket which is common practice in hanging T.V. sets from walls or ceilings in hospitals cause extreme electrical hazards.
The ground fault indicator would be okay, except it must be so sensitive to current leak below dangerous current levels that it will break circuits for other reasons than those of safety and the false interruptions are a nuisance and a hazard if you are depending on the appliance. The visible indicators do not protect against one using the appliance and achieve only limited safety. All of these safety methods have their positive attributes provided there is no circumscribing of the intended safety as a matter of economy, convenience, or through necessity.